Micromembrane actuator

Abstract

Thin film shape memory alloy (SMA) micro pump that has high work density and high frequency response. A miniature SMA pump is used to rectify liquid to achieve stroke. Controlled fluid flow provides forced convection cooling on the SMA membrane that allows the micro pump to operate at high operational frequencies and high work density.

1 . An actuator mechanism comprising: 
 an actuator body comprising an actuation chamber having a membrane seat surface;    a membrane comprising a shape memory alloy that has a martensite-austenite transition temperature, said membrane being located over said membrane seat surface to define a pump chamber between said membrane seat surface and said membrane, said membrane being movable from an undistorted form to a distorted form;    at least one inlet through which fluid is introduced into said pump chamber;    at least one outlet through which fluid is removed from said pump chamber, said outlet being located at a spaced location from said inlet;    a bias pressure applicator that introduces said fluid into said pump chamber at a temperature that is below said martensite-austenite transition temperature; and    a heating system that heats said membrane to an actuation temperature that is above said martensite-austenite transition temperature when said membrane is in said distorted form.    
   
   
       2 . An actuator mechanism according to  claim 1  comprising at least two outlets through which fluid is removed from said pump chamber.  
   
   
       3 . An actuator mechanism according to  claim 1  wherein said inlet is located centrally in said membrane seat surface and said outlet is located towards a perimeter region of said membrane seat surface.  
   
   
       4 . An actuator mechanism according to  claim 2  wherein said inlet is located centrally in said membrane seat surface and said outlets are located towards a perimeter region of said membrane seat surface.  
   
   
       5 . An actuator mechanism according to  claim 4  wherein said membrane seat surface has a circular perimeter.  
   
   
       6 . An actuator mechanism according to  claim 1  wherein said membrane seat surface is in the form of a dome that extends inwardly into said actuation chamber.  
   
   
       7 . An actuator mechanism according to  claim 6  wherein said dome has a center and said inlet is located in the center of said dome.  
   
   
       8 . An actuator mechanism according to  claim 7  wherein said dome has a perimeter, and said outlet is located towards the perimeter of said dome.  
   
   
       9 . An actuator mechanism according to  claim 6  wherein said dome has a perimeter, and at least two outlets are located in said membrane seat surface and located towards the perimeter of said dome.  
   
   
       10 . An actuator mechanism according to  claim 9  wherein said outlets are spaced equidistantly around the perimeter of said dome.  
   
   
       11 . An actuator mechanism according to  claim 1  wherein said heating system includes a system for applying an electrical current to said membrane to provide heating thereof.  
   
   
       12 . An actuator mechanism according to  claim 30  wherein said inlet flow control mechanism comprises an inlet pressure check valve that prevents flow of fluid from said pump chamber out through said inlet when said fluid in said pump chamber is under a pumping force exerted by said membrane.  
   
   
       13 . An actuator mechanism according to  claim 31  wherein said outlet flow control mechanism comprises an outlet pressure check valve that prevents flow of fluid from said outlet back into said pump chamber wherein said fluid in said pump chamber is under a bias force exerted by said bias pressure applicator.  
   
   
       14 . A method for pumping fluid comprising the steps of: 
 A) providing an actuator mechanism comprising:    an actuator body comprising an actuation chamber having a membrane seat surface;    a membrane comprising a shape memory alloy that has a martensite-austenite transition temperature, said membrane being located over said membrane seat surface to define a pump chamber between said membrane seat surface and said membrane, said membrane being movable from an undistorted form to a distorted form;    at least one inlet through which the fluid to be pumped is introduced into said pump chamber;    at least one outlet through which said fluid is removed from said pump chamber, said outlet being located at a spaced location from said inlet;    B) introducing said fluid into said pump chamber at a temperature that is below said martensite-austenite transition temperature and at a bias force, and    C) heating said distorted membrane to an actuation temperature that is above said martensite-austenite transition temperature to exert a pumping force against the fluid in said fluid chamber.    
   
   
       15 . A method for pumping fluid according to  claim 14  wherein at least two outlets are located in said membrane seat surface.  
   
   
       16 . A method for pumping fluid according to  claim 14  wherein said inlet is located centrally in said membrane seat surface and said outlet is located towards a perimeter region of said membrane seat surface.  
   
   
       17 . (canceled)  
   
   
       18 . (canceled)  
   
   
       19 . A method for pumping fluid according to  claim 14  wherein said membrane seat surface is in the form of a dome that extends inwardly into said actuation chamber.  
   
   
       20 . (canceled)  
   
   
       21 . (canceled)  
   
   
       22 . A method for pumping fluid according to  claim 19  wherein said dome has a center and a perimeter, and said inlet is located in said center, and at least two outlets are located in said membrane seat surface and located towards the perimeter of said dome.  
   
   
       23 . (canceled)  
   
   
       24 . A method for pumping fluid according to  claim 14  wherein said heating of said distorted membrane is accomplished by passing an electrical current through said membrane.  
   
   
       25 . In a method for pumping a fluid wherein a membrane comprising a shape memory alloy is repeatedly heated and cooled, the improvement comprising forced convective cooling of said membrane by introducing a pressurized flow of said fluid into contact with said membrane at an inlet location and flowing said liquid over said membrane to an outlet location that is spaced from said inlet location.  
   
   
       26 . An improved method for pumping fluid according to  claim 25  wherein said fluid is flowed from said inlet location over said membrane to at least two outlet locations.  
   
   
       27 . An improved method for pumping fluid according to  claim 26  wherein said inlet location is located at the center of the membrane and the outlet locations are located around the perimeter of the membrane.  
   
   
       28 . An improved method for pumping fluid according to  claim 27  wherein said outlet locations are located equidistantly around the perimeter of said membrane.  
   
   
       29 . An actuator mechanism according to  claim 1  wherein said actuator body includes at least two actuation chambers.  
   
   
       30 . An actuator mechanism according to  claim 1 , wherein the bias pressure applicator introduces said fluid into said pump chamber at a bias force that is sufficient to move said membrane from the undistorted form to the distorted form.  
   
   
       31 . An actuator mechanism according to  claim 30 , wherein said membrane at said actuation temperature exerts a pumping force against the fluid in said fluid chamber that is greater than the bias force applied to said fluid by said bias pressure actuator to thereby move fluid out of said pump chamber through said outlet.  
   
   
       32 . A method for pumping fluid according to  claim 14 , wherein said step of introducing said fluid into said pump chamber comprises introducing said fluid into said pump chamber at a bias force that is sufficient to move said membrane from the undistorted form to the distorted form.  
   
   
       33 . A method for pumping fluid according to  claim 32 , wherein the pumping force exerted by the membrane is greater than the bias force.